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1. Field of the Invention
The present invention relates generally to molded articles with elongated metallic cores. More particularly the present invention pertains to rotomolded thermoplastic articles, such as window wells and manholes, with integrally molded ladders with rungs that include metallic cores, and both method and apparatus for making.
2. Description of the Related Art
Window wells serve a purpose that is included in their name. They are a well, or hole in the ground, that is juxtaposed against a window, and that allows light to reach a window. However, when there is human occupancy below grade, it is important to provide a way of escape in the event of fire, or other disaster.
Providing larger windows in a lower-level room allows the use of larger window wells, and providing windows that are higher not only allows more sunlight to enter, but also requires larger window wells.
As windows and window wells become larger, and particularly higher, they provide an excellent path for emergency egress, in that children and adults may literally step out of the room into the window well and up to safety.
However, with deeper window wells, some children, and some adults may not be able to climb out of the window well. To escape a burning building, but to be trapped in a window well, is not a satisfactory way of escaping a fire, and the laws of an increasing number of states are providing requirements for built-in ladders.
To meet the need for ladders in window wells, some manufacturers of galvanized steel window wells have riveted-ladders into their window wells, and one manufacturer of molded plastic window wells has molded terraced steps into the window well distal from the window.
While both galvanized window wells with ladders and molded plastic window wells have provided useful products, the riveted-ladder window well may fail due to rust, and the terraced-step window well is excessively expensive to manufacture, and does not provide egress that is as safe as that provided by a ladder with rungs that can be grasped by the hands of children and the hands of arthritic adults.
A wall and ladder structure, which may be in the form of such articles as a window well or a manhole, includes a thermoplastic wall, a plurality of ladder rungs that include both hollow metallic cores that are thermoplastically attached to the wall, and a thermoplastic sleeve that covers each of the metallic cores and that is integral with the thermoplastic wall.
The method of making the wall and ladder structure includes: placing a quantity of a thermoplastic inside a mold, heating the mold, rotating the heated mold, disposing at least a portion of a hollow metallic core inside the mold, flowing heated air through the hollow metallic core during at least a portion of time wherein the rotating step is performed, and bonding a layer of the thermoplastic onto the hollow metallic core during at least a portion of the rotating step.
The mold apparatus includes an exterior-contour mold, or thermoplastic rotomold, a hollow metallic core, being at least partially disposed inside the mold, that provides a healing passage therein that includes an inlet and that includes an outlet that communicates with furnace air outside the mold, and an air supply port being connected to the inlet.
In a first aspect of the present invention, a method for rotomolding a thermoplastic article which comprises placing a quantity of a thermoplastic inside a rotomold, heating the rotomold, and rotating the heated rotomold, the improvement comprises: disposing at least a portion of a metallic core, that includes a heating passage, in the rotomold; flowing heated air through the heating passage during at least a portion of time wherein the rotating step is performed; bonding a layer of the thermoplastic onto the metallic core during at least a portion of the rotating step; the disposing step comprises providing a pair of openings through the rotomold, and clamping the metallic core with respect to the rotomold; and the flowing step comprises communicating the heated air through one of the openings and into the heating passage, and communicating the heated air from the heating passage through the other of the openings to air outside the rotomold.
In a second aspect of the present invention, a method for rotomolding a thermoplastic article which comprises placing a quantity of a thermoplastic inside a rotomold, heating the rotomold, and rotating the heated rotomold, the improvement comprises: disposing at least a portion of a metallic core, (hat includes a heating passage, in the rotomold; flowing heated air through the heating passage during at least a portion of time wherein the rotating step is performed: bonding a layer of the thermoplastic onto the metallic core during at least a portion of the rotating step; the disposing step comprises providing first and second openings in the rotomold, inserting first and second clamp bars through respective ones of the openings, and clamping the metallic core between the clamp bars; and the flowing step comprises communicating the heated air into one of the clamp bars and out of another of the clamp bars.
In a third aspect of the present invention, mold apparatus for rotationally molding thermoplastic articles comprises: a thermoplastic rotomold; a hollow metallic core being disposed in the rotomold; and means for flowing hot air through the hollow metallic core.
In a third aspect of the present invention, mold apparatus for rotationally molding thermoplastic articles comprises: a rotomold having a pair of openings therethrough; an elongated metallic core having a heating passage therein, ends and being at least partially disposed inside the rotomold; a clamp bar that includes a longitudinal passage and that extends through the openings to clamp the ends of the metallic core with respect to the rotomold such that the longitudinal passage is in communication with the heating passage; and a hot air passage that includes an inlet port, the heating passage, the longitudinal passage and a transverse passage that communicates air from one of the openings into the heating passage and from the heating passage through another of the openings to air outside the rotomold.